1. Field of the Invention
The present invention relates to an electric vehicle equipped with an electric motor as a traveling motive power source thereof, and a regeneration control method for the electric vehicle.
2. Description of the Related Art
As an electric vehicle provided with an electric motor as a traveling motive power source thereof, there has been known an electric vehicle disclosed in, for example, PCT international publication WO97/10966 (hereinafter referred to as patent document 1) or the publication of Japanese Patent No. 3263844 (hereinafter referred to as patent document 2). In these electric vehicles, regenerative braking of an electric motor is effected when neither accelerator (gas) pedals nor brake pedals are in operation. According to the technique disclosed in patent document 1 or patent document 2, the regeneration amount of the electric motor is determined by multiplying a basic regeneration amount, which is set by a regeneration amount adjusting switch, by a regeneration gain corresponding to an engine brake, which is determined by adding a reference gain set on the basis of the number of revolutions of the electric motor and an increase/decrease gain set on the basis of the gradient of a road surface. Then, a regenerative operation of the electric motor is performed with the determined regeneration amount.
According to the techniques disclosed in the aforesaid patent documents 1 and 2, the increase/decrease gain is uniquely determined on the basis of the gradient of a road surface. Hence, even if the gradient of the road surface remains unchanged, the acceleration generated in the direction in which the vehicle advances when the electric motor runs in a regenerative operation mode tends to vary due to changes in disturbance factors, such as the direction of wind (whether the wind is blowing against the vehicle or following the vehicle) and the number of persons in the vehicle (the total weight of the vehicle). Especially when the vehicle is traveling on a down-slope road, which tends to cause the vehicle speed to increase, variations in the acceleration of the vehicle attributable to the aforesaid changes in disturbance factors are frequently more notable.
Therefore, a braking force of the vehicle generated by the regenerative operation of the electric motor when the vehicle is traveling on a down-slope road is apt to be excessively weak or strong. This has been apt to inconveniently force a driver to frequently step on the brake pedal or the accelerator (gas) pedal of the vehicle to adjust the vehicle speed.